When should someone put education credentials after their names? BS, MBA, MFA, JD, PhD etc etc etc when is it acceptable and at what level?

I think a graduate degree or above is appropriate. I put it in my signature block, and that's about it. I also use only the highest degree earned. I think the highest degree trumps the lower degrees, so adding multiple degrees is unnecessary. I suppose an argument can be made if someone has two terminal degrees (like a PhD and JD, or a PhD and MD).

Decided to go hunt for this answer. Check out https://en.wikipedia.org/wiki/Post-nominal_letters.
Basic answer:

In the United States, standard protocol is to place them in this order:
Religious institutes
Theological degrees
Academic degrees
Honorary degrees, honors, decorations
Professional licenses, certifications and affiliations
Retired uniformed service (active duty service brackets the name – e.g., Firefighter John Doe, CFD – and active duty armed services do not display postnominals other than branch of service)[1]

Common practice is to name only the highest degree in a particular discipline (e.g., if one had earned one's BS, MS, and PhD in Biology – even from different schools – as well as an MBA in Management, then the preferred listing would be John Doe, MBA, PhD).

Context is everything. If you are presenting in front of a body of professionals for example, your highest level in that field should be listed for credibility. I co-facilitate a medical awareness class with a nurse, therefore RN is listed after her name on the PowerPoint. I have a co-worker that is a subject matter expert in her discipline, yet she does not feel the necessity to list the fact that she has a Masters degree.